The language is from the troah. Whether you want to use modern Hebrew or not, the core is still from the Torah. According to the Rambam it's a Mitzvah to speak lashon hakodesh.
The language is most definitely not from the torah, it uses words of the torah and many times contorts their meaning.
In addition, the language was intended with the express purpose of promoting an anti-torah philosophy. That in itself makes it unholy.
The Rambam would be referring to an actual holy tongue, not that trash.
R' Ahron Kotler himself ruled it was assur for the Bais Yaakov to teach in that language.